Hot runner systems include the transfer of a molten material into a mold at high pressures. For plastic injection molding hot runner systems, an injection unit melts pelletized plastic into molten plastic before injecting the molten plastic into a closed mold. In its most basic configuration, the mold includes two halves, a core half and a cavity half, which cooperate to define a mold cavity in the desired shape of a single part. The molten plastic cools and solidifies between the mold halves, and is ejected from the mold cavity as a finished part.
Hot runner systems also include a hot drop for directing the flow of molten material to a valve gate. Hot drops generally include a feed hole and an electrical heating unit, such as a heater band, around a nozzle body. Molten material flows through the hot drop to the valve gate where it enters the mold cavity. A valve pin moves away from and toward the mold opening to open and close the valve gate, respectively, to selectively allow molten material into the mold cavity. This process is repeated for each successive shot of molten material.
In some operations, hot runner systems can leave a witness mark on the finished part generally equal to the valve gate diameter. The witness mark, or other surface imperfection, can also arise in the absence of an even distribution of molten material at the valve gate opening. Accordingly, there remains a continued need for a hot runner system providing an improved distribution of molten material at the valve gate opening. In particular, there remains a continued need for a hot runner system that minimizes the presence of witness marks and other imperfections on the finished part for plastic injection molding and other operations.